Is "750XD" meaning "0.750 inch external diameter"?

Yes, same dia as a mil spec but the shape of the lugs increase the strength.

gatnerd said:

Seems Australia is developing its own 6.8x51 that does not use a 2 part case like SIG:

I wonder if they used the 277 Fury case shape?  Compared to a simple 277-308 wildcat, the Fury has less body taper, sharper shoulder and shorter neck.  This gives a slightly larger propellant capacity for a normal brass case.   Things could change if the case walls get thicker, of course.  It would be interesting to see how high the pressure could be pushed with an optimized brass or steel case.

nincomp said:

I wonder if they used the 277 Fury case shape

I'd be astounded if they weren't copying the same case dimensions given their goal to have some commonality with the US 6.8. 

The SIG Spear seems to have the ability to fire both standard ~60kpsi brass ammo as well as ~80kpsi hybrid ammo, at least from the few youtube clips we've seen.

I imagine the Australians are interested in a similar goal? This domestic case that they can make royalty free, that offers 'general purpose' performance, but retain the ability to fire high pressure US AP when the AUKUS balloon goes up?

All speculation on my part here, I just have that little insta post to go on. 

gatnerd said:

       nincomp said: I wonder if they used the 277 Fury case shape

I'd be astounded if they weren't copying the same case dimensions...

Ditto.

gatnerd said:

This domestic case that they can make royalty free, that offers 'general purpose' performance, but retain the ability to fire high pressure US AP when the AUKUS balloon goes up

Quite logical.

EmericD said:

Is it a crack running around the "6.8x51" mark, and an ejector mark between the "BB" and the kangaroo?

Concur on the mark between the "BB" and the kangaroo being an indentation from the ejector.

I think it is not a crack at the "6.8x51" mark, but perhaps an impression of the extractor groove on the bolt face.

stancrist said:

I think it is not a crack at the "6.8x51" mark, but perhaps an impression of the extractor groove on the bolt face.

Could be. My experience is that the extractor mark is generally found inside the groove, where the extractor try to shear the rim.

Looks like that this case is operating just below the threshold of catastrophic failure.

EmericD said:

My experience is that the extractor mark is generally found inside the groove, where the extractor try to shear the rim.

Not the groove in front of the cartridge case rim.  The groove / channel machined into the bolt, into which the extractor is fitted.

Although to make that shape of impression on the case head, the extractor channel bottom would have to be rounded instead of flat.

Sweden reportedly adopting a new 7.62x51 infantry rifle, with an eye to possible future conversion to 6.8x51.

https://www.ar15.com/forums/General/Sweden-goes-ahead-with-new-service-rifle/5-2633465/#i103427018

https://forums.delphiforums.com/autogun/messages?msg=7952.27

So the list of potential NGSW users is now up to three (US, Australia, Sweden).  Who will be next?  

Didn't Sweden just go with 7.62 NATO?